The present invention relates to range finding devices and methods, and more particularly to those devices and methods which use successive two-dimensional images of a scene to derive range or terrain structure information.
In the past, low flying aircraft or remotely piloted vehicles have utilized an active imaging sensor, for example, a laser or radar scanning device in order to derive range or terrain structure information. Typically, these terrain sensing devices scan the scene with an appropriate energy source, creating a range-image map of the upcoming terrain scene in which the intensity of each sensed pixel is proportional to the range from the active sensor to the corresponding portion of the scene.
These devices have several disadvantages. First, devices using an active imaging sensor will generally be more complex than those using a passive sensor and will, therefore, be more expensive. Second, the addition of a power supply for an active sensor increases the device weight and volume, which is generally undesirable in aircraft applications. Third, when such devices are used in low flying reconnaissance vehicles, the illuminating source used with the sensor may be seen from the ground, thus negating any stealth benefit gained by flying at a low altitude.
It is accordingly a primary object of the present invention to provide a range measurement or terrain mapping device which does not require an active sensor, and which is capable of deriving range information in real time as required by low flying aircraft or terrain following vehicles.